Commitments and Contingencies (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012 sites	Aug. 18, 2011 bbl
Commitments and Contingencies (Textual) [Abstract]
Site contingency number of sites checked	6
Number of sites requiring remediation and water contamination as per phase two investigations	4
Accrued liability, estimated fines and environmental contributions	0.4
Asset retirement obligation liability	39.7
Estimated cost to retire facilities	109.1
SemCrude Pipeline [Member]
Commitments and Contingencies (Textual) [Abstract]
Loss contingency claims, number of barrels of crude oil owed		141,000
Site contingency number of sites checked	5
SemGas [Member]
Commitments and Contingencies (Textual) [Abstract]
Site contingency number of sites checked	1
Due under the contract	0.1
Future obligations	3.3
Future obligations related to processing facility	6.6
Minimum [Member]
Commitments and Contingencies (Textual) [Abstract]
Notice required to cancel purchase agreements, days	30 days
Maximum [Member]
Commitments and Contingencies (Textual) [Abstract]
Notice required to cancel purchase agreements, days	120 days